The barrel of the tumbler pictured is 6-3/4 inches deep by 5-1/2 inches in diameter and it holds 14 cups of water (without steel shot). This unit was actually designed for lapidary (stone) tumbling, and is much larger than units designed for jewelry. Rio Grande (jewelry supply company) recommends filling rotary barrels half-full with tumbling media, which for my unit would mean over 10 pounds of shot! Three pounds seems to work just fine for my work. As with many things, "your mileage may vary."